Well I don't drive the jeep on a regular basis, but I keep a large rubbermaid box in the back of my yukon with many items for almost any scenario...
First Aid Kit, Jumper Cables, many tools (well planned to be able to fix mine or someone elses problems), flares, 1 gallon jug of compacted ashes (to throw down for traction in the snow), flares, 2 hitches (1 with 3 sizes of balls, 1 with 6" drop 2" ball), para cord / rope, 6 MREs, tow strap, come along, misc budgie cords, misc motorcycle tie down straps, gerber hatchet/hammer, warm gloves, leather work gloves, gerber shovel, spare set of clothing, and old work boots (dry with dry socks!!!)... probably a couple of other things I am not thinking of...
There are also a number of things that stay in the truck. ruger 10/22 with 100 rounds, spare cell phone with one of those energizer battery powered chargers...this would allow me to simply put my sim card in the spare phone, and good to go, 5" folding knife, spare batteries AA and AAA, built in nav, but carry maps, AAA card, $200 cash and a credit card hidden well (incase of a mugging or something of that sort), my yukon also had an empty battery tray in the engine bay, so I put a spare battery in there (fully charged), incase I need to jump myself... again, theres probably some things im missing.
On my person at all times, wallet, cell phone, glock 17, spare mag, surefire flashlight, folding pocket knife, keys, and chap stick (maybe the most important thing to me this time of year!)